DESCRIPTION (applicant's abstract): We propose to study neurophysiological mechanisms mediating the regulation of serotonin-containing neurons in the mammalian dorsal raphe nucleus (DRN) by the hypnogenic system in the preoptic hypothalamus and adjacent basal forebrain (POA/BF). Activation during spontaneous sleep of warm-sensitive neurons (WSNs) and deactivation of cold-sensitive neurons (CSNs) plays a critical role in the POA/BF hypnogenic process. WSNs and CSNs are identified by responses to local warming and cooling. Previous evidence shows that the POA/BF also contains both REM-facilitatory and REM-inhibitory processes. Suppression of DRN serotonergic neuronal discharge was shown to play a role in both NREM sleep onset and REM sleep triggering. Recent anatomical and physiological evidence shows that activation of the POA/BF WSN/CSN hypnogenic system can induce suppression of DRN neuronal activity, suggesting a mechanistic basis for NREM-REM coordination. We have developed a testable 2-stage model of regulation of DRN and REM triggering by the POA/BF. Aim 1 is to quantify the regulation of REM sleep control by POA/BF temperature-sensitive neurons. Aim 2 is to use microdialysis to confirm that POA/BF warming induces increased release of the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA) in DRN, and that postsynaptic blockade of GABA in DRN prevents POA/BF-induced changes in NREM EEG deactivation and REM-triggering. Aim 3 will combine microdialysis and neuronal unit recording in the DRN to assess hypotheses that GABA release induced by POA/BF warming regulates DRN neuronal discharge and that DRN neuronal discharge regulates REM triggering. Aim 4 will use techniques to generate REM-enriched sleep and the method of proto-oncogene c-fos expression to label neuronal activity in order to assess a hypothesis that a subregion of the POA/BF, the peri-ventrolateral preoptic area (peri-VLPO) contains REM-selective neurons. Aim 5 is confirm the existence of REM-selective neurons in peri-VLPO using chronic neuronal unit recording techniques. Aim 6 is to use microdialysis of a GABA agonist, muscimol, to inactivate the peri-VLPO area to assess the hypothesis that this region is essential for REM-triggering. These studies will provide a new model of interactions of NREM and REM sleep mechanisms and will contribute to the understanding of human diseases including narcolepsy and affective disorder in which NREM-REM coupling is disordered.